Tiki 26 Changing Secifications Aluminum Mast

Could I get away with using a standard (oval) aluminium mast section with internal track for the wing sail which has been recommended by Rolly Tasker rigging dept? The specified aluminium tube is not available localy. The closest I could find was 140mm diameter 4mm wall. Too big? The specs in the plans are for 127 diam 2.5mm thickness. Could I go smaller 101diam ith slightly thicker wall of 3mm?.... Cheers Pat. Attached is mast sec. available locally Rollt Tasker Thailand